As is know in the art, satellite navigation systems, such as the global positioning system (GPS), enable a receiver to determine a location from ranging signals received from a plurality of satellites. Position can be determined from code and/or carrier phase information. A code division multiple access (CDMA) code is transmitted by the GPS satellites at 1 MHz for civilian applications and 10 MHz for military applications. The codes from the GPS satellites are correlated with replica codes to determine ranges to different satellites. Accuracy is enhanced using real-time kinematic processing of carrier phase information.
Exemplary techniques for carrier phase integer ambiguity resolution or fixing are shown and described in U.S. Pat. No. 7,205,939 to Zimmerman, U.S. Pat. No. 6,753,810 to Yang et al, and U.S. Pat. No. 6,697,736 to Lin, all of which are incorporated herein by reference. Accuracy at the level of tens of centimeters is possible with real-time kinematic (RTK) carrier phase integer ambiguity resolution.
As is known in the art, certain applications require very accurate positional location information. For example, inflight aircraft refueling requires precise positioning for successful operations. Prior art navigation techniques for such applications include double difference-based architectures that employ real-time kinematics. While such systems may be adequate for some applications, other applications, such as precision approach and landing systems and autonomous airborne refueling may have more demanding navigation and integrity requirements unmet by existing systems.